For ecological and economic reasons the paint industry is attempting to replace as large as possible a portion of the organic solvents employed in paints by water. In the context of automotive finishing in particular, there is a great requirement for aqueous coating materials. This applies both to the area of production-line automotive finishing and to the area of automotive refinishing.
EP-B-0 358 979 discloses aqueous two-component polyurethane coating compositions which comprise a hydroxyl-containing polyacrylate resin dispersed in water, and a polyisocyanate component. These coating materials described in EP-B-0 358 979, however, exhibit great disadvantages in respect of gloss, relaxation (low graininess of the coating), boil-mark tendency and, resulting therefrom, spray safety, and in respect of weathering resistance, especially in respect of resistance under constant condensation conditions (40 degrees C., 240 hours), processibility (drop in viscosity and inadequate pot life) and hardness.
The object of providing an aqueous coating composition which has improved properties and/or which gives improved coating films relative to the aqueous two-component polyurethane coating compositions known from EP-B-0 358 979 is largely achieved by the as yet unpublished German Patent Application P 44 21 823.0. Nevertheless, even using the 3-component systems in accordance with the as yet unpublished German Patent Application P 44 21 823.0 as automotive refinishes, there are still problems on the fully cured coatings as a result of boil marks, grey haze and/or textured surfaces, caused by poor leveling of the coating compositions.
The object which results from this, namely to provide coating systems for automotive refinishing which under the conditions of automotive refinishing lead to coatings which exhibit no surface problems, such as boil marks or textures, and no impairment of the optical quality, such as grey haze, is achieved by the 3-component coating composition described in the as yet unpublished German Patent Application P 195 42 626.
These 3-component coating compositions are characterized in that
1.) component (I) contains as binder (A) PA1 2.) component (II) contains as crosslinking agent (F) at least one di- and/or polyisocyanate (F1) which is optionally dispersed or dissolved in one or more organic solvents, and/or optionally at least one further crosslinking agent, consisting of at least one epoxide compound (F2) having at least two epoxide groups per molecule and/or optionally at least one amino resin (F3), and PA1 3.) component (III) comprises components (A1) and/or (A2) and/or (A3) and/or (A4) in aqueous dispersion. PA1 (aa1) an essentially carboxyl-free (meth)acrylic ester which is different from (aa2), (aa3) and (aa4) and is copolymerizable with (aa2), (aa3) and (aa4), or a mixture of such monomers, PA1 (aa2) an ethylenically unsaturated monomer which is copolymerizable with (aa1), (aa3) and (aa4), carries at least one hydroxyl group per molecule and is essentially free from carboxyl groups, PA1 (aa3) optionally an ethylenically unsaturated monomer which is copolymerizable with (aa1), (aa2) and (aa4), is different from (aa1), (aa2) and (aa4) and is essentially free from carboxyl groups, or a mixture of such monomers, and PA1 (aa4) an ethylenically unsaturated monomer which carries at least one carboxyl group per molecule and is copolymerizable with (aa1), (aa2) and (aa3), or a mixture of such monomers, is prepared by subjecting the aqueous dispersion of the hydrophobic polymer resin HP' and the aqueous emulsion of the monomeric constituents to high shear and subsequently the polymerizable constituents of the preemulsion PE are polymerized. PA1 I. in deionized water, a preemulsion PE comprising microparticles consisting of the hydrophobic polymer resin HP' and the monomeric constituents PA1 II. during and/or after the conclusion, but not simultaneously with the commencement, of the polymerization of the polymerizable constituents of the preemulsion PE, a monomer mixture comprising PA1 (A1) at least one acrylate copolymer (A1) which is dispersed or dissolved in one or more organic, optionally water-dilutable solvents, contains hydroxyl groups and acid groups which can be converted into the corresponding acid anion groups and preferably has a number-average molecular weight Mn of between 1,000 and 30,000 daltons, an OH number of from 40 to 200 mg of KOH/g and an acid number of from 5 to 150 mg of KOH/g, and/or PA1 (A2) at least one polyester resin (A2) which is dispersed or dissolved in one or more organic, optionally water-dilutable solvents, contains hydroxyl groups and acid groups which can be converted into the corresponding acid anion groups and preferably has a number-average molecular weight Mn of between 1,000 and 30,000 daltons, an OH number of from 30 to 250 mg of KOH/g and an acid number of from 5 to 150 mg of KOH/g, and/or PA1 (A3) at least one polyurethane resin (A3) which is dispersed or dissolved in one or more organic, optionally water-dilutable solvents, contains hydroxyl groups and acid groups which can be converted into the corresponding acid anion groups and preferably has a number-average molecular weight Mn of between 1,000 and 30,000 daltons, an OH number of from 20 to 200 mg of KOH/g and an acid number of from 5 to 150 mg of KOH/g, and/or PA1 (A4) optionally a further binder. PA1 a1) an essentially acid group-free (meth)acrylic ester which is different from (a2), (a3), (a4), (a5) and (a6) and is copolymerizable with (a2), (a3), (a4), (a5) and (a6), or a mixture of such monomers, PA1 a2) an ethylenically unsaturated monomer which carries at least one hydroxyl group per molecule and is essentially free from acid groups, is copolymerizable with (a1), (a3), (a4) , (a5) and (a6) and is different from (a5), or a mixture of such monomers, PA1 3) an ethylenically unsaturated monomer which carries at least one acid group, which can be converted into the corresponding acid anion group, per molecule and is copolymerizable with (a1), (a2), (a4), (a5) and (a6), or a mixture of such monomers, and PA1 a4) optionally one or more vinyl esters of alpha-branched monocarboxylic acids having 5 to 18 carbon atoms per molecule, and/or PA1 a5) optionally at least one reaction product of acrylic acid and/or methacrylic acid with the glycidyl ester of an alpha-branched monocarboxylic acid having 5 to 18 carbon atoms per molecule or, instead of the reaction product, an equivalent quantity of acrylic and/or methacrylic acid which is then reacted, during or after the polymerization reaction, with the glycidyl ester of an alpha-branched monocarboxylic acid having 5 to 18 carbon atoms per molecule, and PA1 a6) optionally an ethylenically unsaturated monomer which is copolymerizable with (a1), (a2), (a3), (a4), and (a5), is different from (a1), (a2), (a4) and (a5) and is essentially free from acid groups, or a mixture of such monomers, PA1 (a1), (a2), (a3), (a4), (a5) and (a6) being selected in nature and quantity such that the polyacrylate resin (A1) has the desired OH number, acid number and the desired molecular weight. PA1 (a1) from 20 to 60% by weight, preferably from 30 to 50% by weight, of component (a1), PA1 (a2) from 10 to 40% by weight, preferably from 15 to 35% by weight, of component (a2), PA1 (a3) from 1 to 15% by weight, preferably from 2 to 8% by weight, of component (a3), PA1 (a4) from 0 to 25% by weight, preferably from 0 to 15% by weight, of component (a4), PA1 (a5) from 0 to 25% by weight, preferably from 0 to 15% by weight, of component (a5), and PA1 (a6) from 5 to 30% by weight, preferably from 10 to 20% by weight, of component (a6), PA1 the sum of the proportions by weight of components (a1) to (a6) being in each case 100% by weight. PA1 p1) polycarboxylic acids or their esterifiable derivatives, together if desired with monocarboxylic acids, PA1 p2) polyols, together if desired with monools, PA1 p3) optionally further modifying components, and PA1 p4) optionally a component which is reactive with the reaction product of (p1), (p2) and, if used, (p3). PA1 (A1) at least 20% by weight of at least one acrylate copolymer (A1), PA1 (A2) from 0 to 30% by weight of at least one polyester (A2), PA1 (A3) from 0 to 80% by weight of at least one polyurethane resin (A3), and PA1 (A4) from 0 to 10% by weight of at least one further binder (A4), the sum of the proportions by weight of components (A1) to (A4) being in each case 100% by weight. PA1 (A) from 20 to 90% by weight, preferably from 35 to 80% by weight, of the binder (A), PA1 (B) from 0 to 60% by weight of at least one pigment and/or filler, PA1 (C) from 5 to 50% by weight, preferably from 10 to 40% by weight, of at least one organic, optionally water-dilutable solvent, and PA1 (D) from 0 to 20% by weight, preferably from 0.1 to 10% by weight, of at least one neutralizing agent PA1 E) from 0 to 20% by weight, preferably from 2 to 10% by weight, of at least one customary auxiliary and/or additive, PA1 the sum of the proportions by weight of components (A) to (E) being in each case 100% by weight, based on component (I). PA1 (F) from 50 to 100% by weight, preferably from 60 to 90% by weight, of at least one crosslinking agent (F), PA1 (G) from 0 to 50% by weight, preferably from 10 to 40% by weight, of at least one organic, optionally water-dilutable solvent, and PA1 (H) from 0 to 20% by weight, preferably from 0 to 10% by weight, of at least one customary auxiliary and/or additive, PA1 the sum of the proportions by weight of components (F) to (H) being in each case 100% by weight, based on component (II). PA1 I. in deionized water, a preemulsion PE comprising microparticles consisting of the hydrophobic polymer resin HP' and the monomeric constituents PA1 is added in a feed stream and then polymerized. PA1 from 60 to 99% by weight of (aa1), PA1 from 1 to 20% by weight of (aa2), and PA1 from 0 to 20% by weight of (aa3), PA1 from 30 to 98% by weight of (aa1), PA1 from 1 to 30% by weight of (aa2), PA1 from 0 to 20% by weight of (aa3) and PA1 from 1 to 20% by weight of (aa4),
(A1) at least one acrylate copolymer (A1) which is dispersed or dissolved in one or more organic, optionally water-dilutable solvents and contains hydroxyl groups and acid groups which can be converted into the corresponding acid anion groups, and/or PA2 (A2) at least one polyester resin (A2) which is dispersed or dissolved in one or more organic, optionally water-dilutable solvents and contains hydroxyl groups and acid groups which can be converted into the corresponding acid anion groups, and/or PA2 (A3) at least one polyurathane resin (A3) which is dispersed or dissolved in one or more organic, optionally water-dilutable solvents and contains hydroxyl groups and acid groups which can be converted into the corresponding acid anion groups, and/or PA2 (A4) optionally at least one further binder, PA2 the binders (A1) and/or (A2) and/or (A3) and/or (A4) being selected such that a 50% strength solution of the binder (A) in ethoxyethyl propionate has a viscosity of &lt;=6.0 dPa.s at 23.degree. C., PA2 (aa1) in essentially carboxyl-free (meth)acrylic ester which is different from (aa2) and (aa3) and is copolymerizable with (aa2) and (aa3), or a mixture of such monomers, PA2 (aa2) an ethylenically unsaturated monomer which is copolymerizable with (aa1) and (aa3), carries at least one hydroxyl group per molecule and is essentially free from carboxyl groups, and PA2 (aa3) optionally an ethylenically unsaturated monomer which is copolymerizable with (aa1) and (aa2), is different from (aa1) and (aa2) and is essentially free from carboxyl groups, or a mixture of such monomers, PA2 is prepared by subjecting the aqueous dispersion of the hydrophobic polymer resin HP' and the aqueous emulsion of the monomeric constituents to high shear and subsequently the polymerization of the polymerizable constituents of the preemulsion PE is begun, and then PA2 (aa1) an essentially carboxyl-free (meth)acrylic ester which is different from (aa2), (aa3) and (aa4) and is copolymerizable with (aa2), (aa3) and (aa4), or a mixture of such monomers, PA2 (aa2) an ethylenically unsaturated monomer which is copolymerizable with (aa1), (aa3) and (aa4), carries at least one hydroxyl group per molecule and is essentially free from carboxyl groups, PA2 (aa3) optionally an ethylenically unsaturated monomer which is copolymerizable with (aa1), (aa2) and (aa4), is different from (aa1), (aa2) and (aa4) and is essentially free from carboxyl groups, or a mixture of such monomers, and PA2 (aa4) an ethylenically unsaturated monomer which carries at least one carboxyl group per molecule and is copolymerizable with (aa1), (aa2) and (aa3), or a mixture of such monomers is added in a feed stream and then polymerized.
The coating compositions described in the as yet unpublished German Patent Application P 195 42 626.6 achieve the objects addressed at the outset outstandingly.
However, there continues to be a need for aqueous coating compositions having improved water resistance, especially toward condensation, and, in particular, having an improved, i.e. accelerated, drying behavior.